1. Field of the Invention
The present invention relates generally to a pre-combustion chamber system for improving the ignition efficiency of an existing internal combustion engine. More particularly it relates to such a system and method in which a pair of specially designed, water cooled pre-combustion chambers are attached to a slow speed reciprocating natural gas engine via the existing cylinder head spark plug holes to provide a pair of high efficiency torch ignition sources for each cylinder.
2. Description of the Related Art
Internal combustion engines which use high volatility fuels such as gasoline or natural gas have traditionally relied upon spark ignition systems. Such spark ignition systems provide adequate ignition energy for most internal combustion engine operating conditions and are particularly effective when the engine is operating at or near full load. However, for certain engines, particularly large, static, natural gas fired engines, traditional spark ignition systems prove inadequate when these engines are operating at less than full load. During operations at less than peak capacity, their fuel governing systems automatically lean out the fuel/air mixture supplied to their cylinders, yielding a fuel mixture with a high ration of air to fuel. Traditional spark ignition systems simply do not provide sufficient ignition energy to ignite such lean mixtures. As a result, large natural gas fired engines operating at lean mixtures tend to experience detonation, misfire, poor fuel economy, and higher emissions of NO.sub.x such as nitric oxide NO and nitrogen dioxide NO.sub.2.
One method for countering the undesirable effects of operating large gas fired engines at lean mixtures involves the use of a pre-combustion chamber, often referred to as a torch ignition source. Pre-combustion chambers typically intake a rich fuel air mixture and ignite it using an ordinary spark plug. The result is a burning fuel mixture which is thrust out an exhaust port and into the engine cylinders at high velocity, much like a blow torch. The high velocity flame ignites the lean fuel air mixture within the cylinder.
These pre-combustion chambers for internal combustion engines have been in use for some fifty years. Pre-combustion chambers are relatively small volume chambers which are placed in communication with a corresponding cylinder in the engine. Pilot fuel is provided to the pre-combustion chamber to enrich the fuel-air mixture therein, which is then ignited via the spark plug. The resulting explosion in the pre-combustion chamber then provides the above-described blow torch effect to completely ignite the fuel-air mixture in the engine cylinder.
In the past, the primary purpose of such pre-combustion chambers was to promote more complete combustion of the fuel and thereby increase the fuel efficiency of the engine.
Recently, the increasing emphasis on improving air quality, and more particularly, the Congressional Clean Air Act which takes full effect in 1995, have resulted in pre-combustion chambers being examined for the purpose of improving engine exhaust gas emissions. One of the industries most impacted by the exhaust gas emissions limits imposed by the new law is the natural gas pipeline industry.
The pipeline industry is comprised of a number of companies with a nationwide grid of gas pipelines. The companies act as carriers for natural gas producers by pumping natural gas through their pipeline networks from the producers to the ultimate consumers. Most, if not all of these pipeline companies use natural gas fired internal combustion engines to drive compressors in pumping stations to push the gas through their pipelines. A very large number of these engines are "dirty" slow speed reciprocating engines manufactured prior to 1970. Emissions standards mandated under the National Clean Air Act mentioned above, and equivalent or even more restrictive standards being mandated under a number of individual State Clean Air Acts would render these engines obsolete unless they can be modified to comply. Replacement of each existing engine with later manufactured "clean" engines entails a cost of about 2 million dollars. Replacement of all of the "dirty" engines in the nationwide pipeline network would require an investment of billions of dollars. Therefore, pre-combustion chambers are being actively investigated by a number of companies for their potential in permitting these older engines to be modified to meet the new emissions standards.
Prior art attempts to produce compatible pre-combustion chambers have generally involved a substantial modification of the existing engine cylinder heads to accommodate relatively large single pre-combustion chambers. Often the existing spark plug holes, of which there are two per cylinder in most engines, are plugged and the air start hole is used to connect the pre-combustion chamber. This technique not only necessitates a greatly modified and expensive cylinder head, but also means that the engine so modified cannot be air started. The cost per cylinder of modifying a dirty engine using these techniques can run $100,000 or more, thus costing $500,000 to modify a single, five cylinder engine.
It is clear then, that a need exists for an alternative system and method of modifying existing dirty engines to meet current exhaust emissions standards. Such a system and method should preferably require little modification of the existing engine cylinder heads and should be relatively inexpensive. At the same time, the system must be reliable and capable of a long operating life, should require minimal engine down time to install and should result in substantial emission reductions for the engines so modified.